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In spite of its importance in microbiology, information on cryopreservation of marine diatom is limited. An attempt was made to develop cryopreservation procedure of marine diatom resting stage cells which abundantly exist in the bottom sediment of coastal area. Bottom sediment samples from the Seto Inland Sea (Harima-Nada) were used for sub-zero temperature preservation experiment in this study. The condition giving optimal survival of microalgae in cryopreserved sediments was as follows : with sorbitol (1 M) as additives, 1/3 salinity, at －80°C preservation (no pre-cooling). Under this condition, two diatoms, Thalassiosira pseudonana and Nitzschia sp., and some unidentified microalgae were recovered from the sediments, but the vegetative cells of obtained diatoms were not able to be cryopreserved again under the same conditions. Present result suggests that these two diatoms were preserved as resting stage cells in the coastal bottom sediments, and the diatom resting stage cells might be more resistant to cryopreservation than the vegetative cells.

Rearing experiments were carried out to study relationships between feeding materials, feeding methods and increase of soft parts of Corbicula japonica. Artifi cial soy food was very effective for the increase of soft parts. Diatom Thalassiosira pseudonana, one main food of the clams in Lake Shinji, increased the soft part, but the effi ciency was not so high. Two feeding methods, “feeding once a day” and “feeding little by little for 12 hours a day” showed almost the same growth of soft parts under the condition of circular running water.